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    SubjectRe: [PATCH 6/9] drivers: add Contiguous Memory Allocator
    On Fri, Oct 14, 2011 at 04:57:30PM -0700, Andrew Morton wrote:
    > On Thu, 06 Oct 2011 15:54:46 +0200
    > Marek Szyprowski <m.szyprowski@samsung.com> wrote:
    > > +#ifdef phys_to_pfn
    > > +/* nothing to do */
    > > +#elif defined __phys_to_pfn
    > > +# define phys_to_pfn __phys_to_pfn
    > > +#elif defined __va
    > > +# define phys_to_pfn(x) page_to_pfn(virt_to_page(__va(x)))
    > > +#else
    > > +# error phys_to_pfn implementation needed
    > > +#endif
    >
    > Yikes!
    >
    > This hackery should not be here, please. If we need a phys_to_pfn()
    > then let's write a proper one which lives in core MM and arch, then get
    > it suitably reviewed and integrated and then maintained.

    Another question is whether we have any arch where PFN != PHYS >> PAGE_SHIFT?
    We've used __phys_to_pfn() to implement that on ARM (with a corresponding
    __pfn_to_phys()). Catalin recently added a cast to __phys_to_pfn() for
    LPAE, which I don't think is required:

    -#define __phys_to_pfn(paddr) ((paddr) >> PAGE_SHIFT)
    +#define __phys_to_pfn(paddr) ((unsigned long)((paddr) >> PAGE_SHIFT))

    since a phys_addr_t >> PAGE_SHIFT will be silently truncated if the passed
    in physical address was 64-bit anyway. (Note: we don't support > 32-bit
    PFNs).

    So, I'd suggest CMA should just use PFN_DOWN() and be done with it.


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